Rubber articles having natural rubber or a diene-based synthetic rubber as a raw material generally deteriorate over time and suffer from crack formation at the surface thereof when exposed to an environment in which ozone is present. Such cracks propagate as the rubber article is subjected to static stress and dynamic stress, and may eventually result in rupturing of the rubber article.
In order to prevent and inhibit the formation and propagation of cracks in a rubber article due to ozone, particularly in the case of tread rubber or sidewall rubber of a tire, it has become common practice to use a rubber composition that contains an anti-aging agent such as N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (PTL 1 and 2).